Automatic sphygmomanometer



s. R. GILFORD AUTOMATIC SPHYGMOMANOMETER Man'ch 18, 1958 Filed sept. 3o,1954 QMII mi d

../ NWS@ mvENToR Saul K. Gilford BY m VW ATTORNEY Ys. R. Glu-'ORD2,827,040

AUTOMATIC SPHYGMOMANOMETER 6 Sheets-Sheet 2 March 1s; 19558 Filed Sept.30, 1954 March 18, 1958 s. R. Glu-ORD 2,327,040

AUTOMATIC SPHYGMOMANOMETER Filed sept. so, 1954 e sheets-sheet s 50u/vnCHAN/v51. AMPL/F/ER X13 DELAY Mv Z2 To To w 5+ N 11a l/l 4@ T' B+PRESSURE CHANNEL AMPLIFIER 8 MULTVBRTOKZJ f 0 K i T0114 THE/@#4157012 48iii i; zg. f77- INVENTOR Jau! E. Gl'lfoPc BY m @7% ATTORNEY 6Sheets-Sheet 4 ATTORNEY Marchls, 1958 s. R. GILFORD AUTOMATICSPHYGMOMANOMETER Filed sept. 30, 1954 BY l ll es Fig. 5-5

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` ATTORNEY March S, 1958 s, R, SALFORD Z@ AUTOMATIC SPHYGMOMANOMETERFiled Sept. 30, 1954 6 Sheets-Shc-ze'kl 6 60 RELA Tn/E l RESPONSE l0 ZO'50 FREQUl/VOCV 200 500 i000 CYCLES Hg 4 P5 @UFF la massif/eg PD l AMROUTPUT t l l l f l z RELAY 1 I j THRU 5 RELAY 5 j 4 5 7 5 INVENTOR Fay,5

@Saul l'lora' BY' M# ATTORNEY United States Patent restare Patented Mar.i, i

AUTOMATIC SPHYGMOMANOMETER Saul R. Gilford, Oberlin, Ohio, assignor tothe United States of America as represented by the Secretary of CommerceApplication September 30, 1954, Serial No. 459,569

16 Claims. (Cl. 12S-2.05)

This invention relates to apparatus for measuring blood pressure andmore particularly to an automatic sphygmomanometer for determining thediastolic and systolic blood pressures of a human being.

Arterial blood pressure in man can be measured in several ways. Onemethod which might be called the direct method is to insert a needle orcannula directly into the artery. A needle or cannula inserted into theartery enables one to bring the pressure out of the system, wherebyemploying one of several specially designed mauometers it is possible todynamically record the cyclic pressure variations in the vessel. As aroutine procedure, however, this type of measurement is not convenientto make because it is time consuming and because the procedure ofcannulating the artery and maintaining a tight clot and air-free systemrequires skillful technique. Furthermore, it requires that the patientremain immobile, and occasionally causes arterial injury and patientdiscomfort.

Two other methods which might be called indirect methods are ofimportance. They are both concerned with sphygmomanometers and will bereferred to as the pressure method and the sound method. Both methodsare indirect ones in that they are based on the consideration that ow inan artery can be occluded if pressure applied externally to the vesselis equal to or greater than the internal pressure. For most diagnosticwork it is necessary to know only the maximum and minimum excursions ofthe blood pressure and a plot of the complete cyclic variation ot thepressure is not required. The maximum and minimum are denoted as thesystolic and diastolic pressure points, respectively.

The sphygmomanometer is a clinical instrument for measuring the maximumand minimum pressure in the extremities. lt consists of an inflatablecuit which is wrapped around the arm, a manometer for indicatingpressure in the cuit, and an inating bulb. The measurement is made byiniiating the cui until the artery in the arm is occluded.

A major difficulty in prior art devices employing sound detection hasbeen the inability of these sphygmomanometers to dilerentiate thedesired signals from spurious undesired noise. These noise signals aredue to various causes particularly movement of the patient and veryoften work on the bony structure during surgery.

One of the important features of the present invention is to overcomethis drawback by incorporating a system in the sphygmomanometer whichpracticallyeliminates the possibility of an inaccurate measurement beingtaken as a result of the device being unable to distinguish betweendesired sound signals from the artery and noise signals.

One object of this invention is to provide a sphygmomanometer capable ofmeasuring systolic and diastolic pressure with good accuracy andrepeatability.

Another object is to provide an improved automatic sphygmomanometer thatis direct indicating, with an output that can be displayed and recorded.

Another object of this invention is to provide an improved automaticsphygmomanometer which gives a direct indication of the systolic anddiastolic pressure values requiring no interpretation by the observer.

A further object of this invention is to provide an '1-- provedautomatic sphygmomanometer which gives a direct indication and record ofthe systolic and diastolic pressure values requiring no interpretationby the observer.

An additional object of this invention is to provide an improvedautomatic sphygmomanometer which gives a continuous directindication andrecord of the systolic and diastolic pressure values requiring nointerpretation by the observer.

A still further object is to provide an improved auto maticsphygmomanometer which gives a simple direct display of only the mostrecent measurement and will retain this until another measurement ismade.

Still another object is to provide an improved automaticsphygmomanometer that can be simply applied and requires no specialskill.

A further object is to provide an improved automatic sphygmomanometerthat is insensitive to disturbances such as room noise, moderatemovement of the patient, and manipulation of the patient by the surgeonand his assistants.

A still further object is to provide a sphygmomanometer which causes nodiscomfort to the patient, which in etect means that the cuff shouldremain iniiated for a minimum period of time, or no longer than is usualfor manual determinations.

An additional object is to provide a sphygmomanometer that is safe forunattended operation. This means that safeguards are incorporated thatprevent breakdown of equipment from keeping the cu iniiated for longperiods or" time or applying excessive pressures.

Other uses and advantages of the invention will become apparent uponreference to the specitication and drawings.

Fig. l shows a functional block diagram of an embodiment of the presentinvention and Figs. lA-li-I show the functions of various elements ofFig. l;

Fig. 2 is a block diagram of applicants invention showing the relationbetween the electrical system and the measuring apparatus;

Figs. 3A-3C together form a complete schematic diagram of thesphygmomanometer;

Fig. 3D is a chart indicating the arrangement of Figs. 3A-3C;

Fig. 4 shows the response curve for the microphone amplifier portion ofthe circuit shown in Fig. 3A and;

Fig. 5 is a timing diagram showing the positions of the relays of Fig.3C throughout a measuring cycle.

Referring to the drawings in which similar elements are denoted by likereference numerals, Fig. l shows in block form the over-all structure otapplicants system.

A microphone 11 is coupled through a tirst or sound channel ampliercircuit 12 to a coincidence circuit 9. Likewise thermistor signals vialead 7 pass through a second or pressure pulse channel amplifier circuit8 to coincidence circuit 9. The output of coincidence circuit 9 is fedto a verification circuit 13 and also to a relay control circuit 14.This latter circuit functions to control two valves 16 and 19 as well asa compressor inlet valve 2 supplied by a compressor inlet representedgenerally by the numeral 1. Valves to and 19 control the ow of air froman air reservoir L@ into a diastolic pressure meter 17 and a systolicpressure meter Ztl, respectively. Relay control circuit 14 also controlsa deilate valve 18.

A passage 5 permits air to escape to a thermistor pressure impulsedetector 6, the output of which is carried by lead 7. An occluding culi`also coupled to reservoir 3 is shown at 4. Y i

Figs. lA-lH illustrating the functions of certain elements in thesystem. Fig. lA shows the pressure variations occurring inthe systemover an entire cycle of diastolic and systolic blood pressuremeasurements. Figs 1B and 1C illustrate the sound andpressure pulsespicked up in the respective channels while Fig. 1D illustrates Vchart inFig. l is therefore arbitrary, the A indicated calibrations being usefulin correlating the various diagrams.

Reference is now had to Fig. 2 which shows the system of the instantinvention with the electrical circuitry in more 'detailed block form andwith Ylemems correspond` ing to like elements in Fig. l bearing the samenumbers. The sound detected at microphone ll passes through amplifiercircuit 12, a band-pass filter 2l. adelay multi- Vvibrator 22, and apulse shaping multivibrator A23 to coincidence circuit 9, ln thepressure channel pulses from .thermistor 6 are fed through amplifier 8and a second Vpulse shaping multivibrator 24 to coincidence circuit 9.Another pulse shaving multivibrator 26 couples coincidence circuit 9V torelay control circuit 14 shown in'dashed lines and to vertificationcircuit 13. Relay control circuit 14 comprises a first gate 27 coupledto a diastolicpressure recording circuit 31 and a second gate 29 coupledto a systolic pressure recording circuit 38.

VA-'pulse absence `detector28 and an inflate-deflate switch 32 compriseVthe remainder of control circuit 14.

Also shown in Fig. 2 are inflate rate and deate rate valves 36 and 37,respectively for manually controlling the rate at which air is suppliedto and taken from the system. A rapid inflate valve 33 controlled by apressure-sensitive switch 34 providesV for rapid inflation of the systemfrom the air supply at the beginning of a measuring cycle. Likewise aVrapiddellateV valve 39 is provided to rapidly exhaust the system at theend of a cycle.v

Referring nowto Figsj3A-3C which form a single schematic diagram of thecomplete system of the instant invention when arranged as shown in Fig.3D there is Ashown in Fig. 3A a representation'of a human limb 42, 'anoccluding cuff '4,' a microphone 11 with securing means 41, sound cableconnection 147, andthermistor cable connection 48. Air' is `supplied tocuff 4 via line 46.

The remaining portions of i-iig.` 3A show in detail the circuitry of thecorrespondinglylabeled blocks of Fig. 2. The particular circuits of eachblock are conventional and need not be further described.

Fig. 3B shows in Ydetail relay control circuit14, verification circuitl13, Vand the various relays that are controlled. Circuit 14 comprises altrst tube I`1 cathode coupled through a relay R1 to a second Vtube T2.A vtube 311' is coupled to multivibrator 26 of Fig. 3A through lead 56.A ,relay R2 is included in the cathode. circuit of tube T1. Another tubeT with associated resistor 97 and capacitor 96 is coupled toA thecathode of tube T1 through two series resistors .83 vand .98. .A tube.T6 with -acathode relay R3 is also coupled 'to tube T5 through `resistor97. The tubes T5 VandI5wit-lrassociated circuitry constitute the pulseabsence detector Relay control circuit V14 includes another tube' -T7havingfa resistor 76 and a relay R1 connectedr toits cathode.' Alsoincluded in circuit 14 is a delay circuit eomprisingresis- Ytors v91,93, and 94 and capacitor 92, aswell 'as additional components comprisinga resistor 102 and a capacitor 103, the latter being shunted byv anotherrelay R5.

Tube T3 along with resistors 86 and 87 as wellV as capacitor 85comprises the verication circuit 13.

Also shown in Fig. 3B are the various relay switches numbered R1S1,R232, et the rst subscript referring to the relay with which the switch.is associated and the secf ond subscriptreferring to the particularswitch. All the relay switches shown'areV single pole double throwswitches.V W i Y Switch R182 islcoupledtoiswitchRsSg-via leadf66 and toswitch R3S1 via lead 67. Lead 71 couples-switch f R183 to 4resistor 91-Switch. 13251 is surlsd to tubeV T1 by lead 84 and to switch R3S3 by`lead 73. Lead 72 couples switchRaSlto'switch R1S2-and-lead 77 couplesswitch RgSl to switch R451. Leads 74 and 78 couple switchR1S1 to tube T7and resistor` 76, respectively, j while lead 79 eouplesswitch R453Various other leads an@ Congedi@ .l Y. dfawingsafe @numbered @nldshells* he sbr/ilove ff? @ne skilled inthe art.

Fig. '3.C`tshows lead which lcouples switchlhSz i to aiplus 2,4-.voltpower supply '1610. y'A noth'er leadf69 .Coupls SwitCh`R2S2 to vthdisuelta valve Cnil and Lead 64 couples a manual startingswitch S1Y andan I.'ulto` matic starting switch S2 to Ythe, relay ,circuitry V o fFig. 3B. Figi 3C further shows a., positive .Z50-volt power supply-1'01,fa Safety switchltlsl vand a minus 15G-volt. power supply A leadis also shown which couples switch R182 of yFig. 3 B t0 the coil Ao fsystolic valve 19. A leadf1`08 couples switch .RSS2 to the coil ofdellate valve 18 and k another lead 1091oup'les switchrRaSztothe .coil.of inate valve VLeads 111 and 112 proyide couplipgltola variable gaincontrolv potentiometer for sound channel; amplifier 12 4while two leadsV1413 Yand Y114- ,couple the sou1 1d' 1n d `pres- -sure .channelamplifiers -to twoneon tubes Vtor visibly indicating the .presence vofpulses in those amplitiers.- .cycle complete lamp: 81 is indicated asconnectedy Ito switch R581. Lead 116 completes the circuit to switchesS2 an'd'S1 andleadv 106 Y couples switch R581 to the `,coil

.ogfrapid-deaeyuve s. Y

GENERAL DESCRIPTION OF OPERATIQN thermistor V6 acts as .a sensitivetransducer .chang` ing the pressure v'variations .into electricalpulses. i transduced pulses are suppliedto pressure channel amplifier 8by Way fof 'lead'7 and then on to coincidence circuit ISince thepressure hasnot yetreac'hed the, diastolic point .no sounds .arelhear Itcan be Seen Vby,c011f1par-ing "Eigs.' 'lC and 1B ,at-suchtime period,nthat the pulses r# ceived f rom" t:he pressure channel and applied tothe coincidence circuilt"` 9 Vbe/ girl'before sounds ,are4` heard Aand vdie kout afterfthe. `lsound A:111.115,65 havedisappeared. While thepressure channel Ypulses themselvesmay he` r1,1sed 't o .',Systclicpressure' Instead, analicen@ utilizes there@ that essere aaaaofrovariations larising from expansion and'contractioncf the artery due tothe variation in blood ow occur at substantially the same time as thesounds caused by the collapsing artery walls in providing the presentmethod of gating out undesired signals picked up in the sound channel bymicrophone 11. Thus, for example, if movement of the patient introducesa sound pulse into the microphone 11, such pulse cannot be transmittedthrough coincidence circuit 9 unless it occurs at the same time that apressure pulse is transmitted from occluding cuff 4. If the sound pulsedoes not occur at the time of a pressure pulse it is blocked bycoincidence circuit 9.

At an arbitrary point B (Fig. 1A), slightly below the diastolicpressure, the rate of increase of pressure in the system is reduced. Thereduction in pressure rate of increase is brought about by therelatively simple by-pass valve 33, the operation of which will be fullyexplained later. The rapid increase of pressure in the system from A toB is incorporated in the system to shorten the length of time that thecuff remains inflated on the patients arm. At point B the increase inpressure is more gradual until the rst pulse appears at the microphonewhen the pressure reaches the diastolic value of point C.

Upon reception of the lirst sound pulse at period t=4 for example,several operations occur simultaneously. The relay control circuit 14functions to close inflate valve 2 (Fig. 2), so that the pressure in thesystem remains constant as shown by line C--D in Fig. 1A. Likewise relaycontrol circuit 14 serves to open valve 16 so that the system pressuremay be recorded in meter 17. The actuations of valves 2 and 16 aresymbolized in Figs. 1G and 1E, respectively corresponding to t=4.

lt will be further noted from Fig. 1D that reception of the first soundpulse at such period coincident with a pressure pulse activatesverification circuit 13. This circuit incorporates a 1.5 second delay sothat if no second pulse is heard over the microphone after 1.5 seconds,the valve 2 is reopened and valve 16 is closed. In other words, theverification circuit listens for a second gated pulse for a period of1.5 seconds. If no second gated pulse appears in the output of thecoincidence circuit 9, the verication circuit 13 then operates relaycontrol circuit 14 so that the conditions prevailing between points Band C on the pressure curve are restored. In this manner theverification circuit 13 can detect a false pulse (i. e., a pulse such asa spurious noise that does n'ot appear again) and reset the relays sothat the pressure continues to increase until a verified pulse appears.The 1.5 second delay is chosen so that enough time is allowed for asecond pulse to appear even for a patient with a very low pulse rate,such as forty a minute.

Upon verification of the first pulse by reception of a second gatedpulse, the verication circuit 13 is deactivated as shown in Fig. 1D,corresponding to point D (t=) on the pressure curve of Fig. lA. At thesame time relay control circuit 14 closes valve 16 as indicated in Fig.lE with the true diastolic pressure recorded on meter 17 and also opensinate valve 2 as shown in Fig. 1G so that the system pressure resumesits gradual rise represented by line D-E of Fig. 1A.

The pressure gradually rises to the systolic value where, as shown inFig. 1B, the sound pulses disappear. A delay unit in relay controlcircuit 14 previously held inoperative by the sound pulses allows thepressure to increase beyond the systolic value before the delay unitcloses inflate Valve 2 at point E on the pressure curve of Fig. 1A. Atthe same time that valve 2 is closed, deilate valve 18 opens, as shownin Fig. 1H, at t=l6.5 approximately, causing the system pressure toslowly decrease along the line E-F.

At point F (1:20) a sound pulse is again heard, representing thesystolic pressure value. Verification circuit 13 is actuated andfunctions'in a manner similar to that previously described with respectto the diastolic pressure reading.` At the same time deate valve 18closes, maintaining a constant pressure along line F-G, while valve 19opens allowing the systolic pressure to be recorded on meter 20.

Upon verification by a second gated pulse valve 19 closes, permanentlyrecording the systolic pressure in meter 20, and a rapid deate valve 39(Fig. 3C) opens, rapidly deatiug the system pressure to atmosphericpressure.

Sound pulses appearing at microphone 11 are transmitted to amplier 12,and then on to band-pass lter 21. The output of filter 21 is applied todelay multivibrator 22 where the pulses are delayed before being appliedto pulse-shaping multivibrator 23. Multivibrator 22 provides a variabledelay which is adjusted to a value equal to the inherent delay in thepressure channel. From multivibrator 23 the sound pulses are fed tocoincidence circuit 9.

The electrical pulses from thermistor-transducer 6 are amplified in thepressure channel by amplifier S and applied to pulse-shapingmultivibrator 24 where the pulses are shaped and are also applied tocoincidence circuit 9.

It should be noted that the present invention provides two distinctfeatures for distinguishing undesired noise from the desired soundpulses. Very often noises due to the movement of the patient or externalnoise is picked up by the microphone and would ordinarily actuate thecircuit. Applicant almost completely avoids such undesired activation byutilizing the pressure pulses to gate the sound. no pressure pulse isreceived will not pass through the coincidence circuit 9. Secondly, theverification circuit 13 requires that two successive pulses betransmitted through the coincidence circuit within a predeterminedperiod before a permanent recording of the pressure is made.

The output of coincidence circuit 9 is supplied to a third pulse-shapingmultivibrator 26 where the pulses are shaped for application to therelay control circuit 14. The pulses supplied to relay control circuit14 are applied to three separate channels in that circuit as will bedescribed. The signals are applied to verification circuit 13 andlikewise to gate 27, pulse-absence detector 2t; and another gate 29.

Upon reception of two successive diastolic-pressure value pulses theverification circuit opens the gate 27 passing pulses to diastolicrecording circuit 31. Diastolic recording circuit 31 momentarily opensvalve 16, allowing the diastolic pressure to be recorded by meter 17. Atthe same time verification circuit 13 through iniiatedeate switch 32closes valve 2 momentarily holding constant pressure in the system.

As shown in Fig. 2 valve 2 is by-passedV by a rapid inilation valve 33which is controlled by a pressure-sensitive switch element 34. Pressureis rapidly built up in the system from compressor inlet 1 through valve33. However, at point B of Fig. lA pressure-sensitive element 34 reactsto the system pressure and functions to close valve 33. The referred-toreduced rate of system-pressure increase is adjusted by ilow-rate valve36 to give the desired rate of increase near the diastolic pressurevalue.

Actuation of diastolic-recorder circuit 31 readies pulseabsence detector23 for the cessation of pulses as the system pressure arises above thesystolic value.

When pulses are no longer received, the pulse-absence detector 23 aftera short time delay activates the inflatedeflate switch 32 so that inatevalve 2 closes and deiiate valve 18 opens. The deation rate is adjustedby ow rate valve 37. The pulse-absence detector 255 likewise activatessystolic-recorder circuit 38. Now, upon reception of pulses at thesystolic pressure value, verication circuit 13 opens gate 29, allowingsystolic-recorder circuit 35 to momentarily open valve 19 so that thesystolic pressure is recorded by meter 20. During the time of In thisway any sound occurring at a time thatk 17 Y -verication, dea-te .valveZ18 -isfclosed niomentarilylmain- :taining.constant-emessa@inlthesystem.

. f;S.ystolic:recorder circuit` 38 includes ,a slow-acting'relay which,after a short time allowing for all actions-to be completed,-.ope nsrapidfdea'te valve 39iwhich completely exhausts-thesystem andends':the-:measuring-cycle. Y

DETAILEDDESCRIPHQN on Q PERATIQN ,The Yover-all functioningof theapparatus having V'been generally Vdescribed,-fthe 'operation'pthe`various componentsV will -be describedfindetail reference being V madeto jFigs.-3A-3C which formasinjgle schematic when arrangedaccordingtothe'diagram'ofliggSD.

Referring to FigiA, at142jis gshowngenerallythe representation of ahuman arm v vithjthe occludingcui 4 surrounding it and closingojanartery. Also surrounding arm f42-is `a-tape^41Y or Votherfasteningmeansfor securing microphone 171 tothe arm. Air issupplied toljthecuffA-by'means'of tube-which isconnected tothe main reservoir 3. i

.'At.- 47 and'AS .cable connections are :shown for 'the microphonesignal pulses and the jpressure gating pulses, respectively. UThe signalpulses'are received directly from the microphone as'shown."Thepressureivariations in the cu arising from'the variations in bloodowthrough the artery are vtransmitted alongtube'fi to the main' reservoir-3 shownin kliigsSC. The momentary variations in: pressure 5 thusoccurring -inthereservoir 13 cause airv to' be transmitted across-thermistor-transducer 6 (Fig. 3C)" by way of 'nozzle inthereservoir 3.'The passing air causes variations inthe thermistor resistance 'due tothe coolingeefiecteof "the-passing air and these'variations aremanifested as a -voltage signal on lead 52. These signals aretransmittedby means`V of-lead"52jto Vconnection 48' in Fig. -3AandthenceV toethe pressurefchannel amplifier 8.

The 10W level output lof Vthe direct contact type piezoelectric-crystalmicrophone TdtV must be increased by sound channel ampliiier-Zto providesuicient energy to oper- -ate the relaysystem through'whichthe measurement functions of-this instrument are carried out.

VThe sound -amplier sectionv12 is confined to the upper left portionofthe diagram and is a conventional resistorcapacitor coupled type. A-gain of `approximately 8i) decibels is realized from the tirst Atwostages. An additional-stage of gainis Arequired to bring thesignalv'level up by a factor of-iive-hefore going through 3-,section RCfilter network 2L `Fig. '4 shows'the amplitude-frequencycharacteStioforthe amplilierelter system. Since the Idesired signalscontain primarilyjfreqnencies'in a range centered Varound-1GO itisdesirable'toreduce the ampliication attrequencies outside ythis range.`The low-pass iilter produces the gradual roll-offofrthe highfrequencies while the incomplete cathodebypassing and RC time constantscause thelow Afrecpiency degradation.

The output of the iilterris introduced into a signal delay circuit andequalizingcircuit/inthe formofa cathodecoupled. one-shot multivibratorYv22-1consisting of both .halves vof V.tube .V1 .andassociatednetworkTube YJ2 `servesas a buierstage VwhichniakesLthestriggeringof themultivibrator 2 2less dependent on.ti1e-arnplitude.and .waveform 05th@ineming pulses- `The general .charac- .feHSfi'CS 0f amultivibrator'emplgyediauh.mangeurs wellknown and are descrihedfon pagesk877- 91 Vof Electronics Experimental Techniques..by.Ehnore and SandsApublished byllcGraw-I-ill,n 1949. En general. in response to aninitiating pulse such as .Obtained from' filter 2i, such multivibratorwill conductand produce asquare wave output 'for a durationdetermined bythe time constant-of the particular circuit employed as isAwell'rlcnown.

APotentiometer154.shown in EigfA provides a convenient means forselectively determining such time constant.

^ By .utilizing the trailing edge 'of-such Asquare-Wave -a `time delaycorresponding :to .the period .-of duration fof the `square wave output-is achieved.: iIhe lpurpose yof -delay .multivibrator ,2.2 .is tocqmpensatetorhe delay occa-'175 v Ythe drawings.

lsioned iby.1ztube=3161in..which ithe:v pressure` pulses :travel: a-substantial-ldistance between cuf`fr4; and; .signal :transducer I6.VThedelay providedfhy multivibratorZZ':cantine-.con- .trolled`byavariable resisten-54 andtisadjusted tio-provide a: zdelaytintewal.fforrfthezsound '.pulse. associatedawithf a pressure 1pllilsemso.fth'attthey pressure/:pulse I.signal :applied `to coincidence gate'f9iwillfibi-'as 1the .latteru-forfcondmtion priorftoithearrival oflacorrespondingisoundlpulse. lhe delayed.E microphone signa-lstfrombmultivihratorZZJiare V:theirj appliehltoapulseshaping;multiirihratorlll :in-Which ithemierophonetsignalpulses-.are shaped in aproperrform for applicationtocoincidenceicircnit'9.`

."`The1gating:.p11lses receiyedr at eonnection are ampli- :iiedxbyiamplier 8.: andeapplieds iotpulsesshapingvmnlti- -vib`rators24.wheretheyi also; are shaped'.foriapplicationto coincidence. '.cirenit59*t-*Whenrithepulsesgare; .receivedat :ea-'eh ;t uhe of :coincidence`circuit 9.-.inephase;wan i output :is derived theretrom.: :and. applied;sto',v another: pulse-shaping rmultivibratordjniwhichtheroutputxpnl-sesare shaped in esuitablenform; forkapplicationnizia.leactf to; the; control circuiteshown generally-.at 14,.:,appearing,iniiFig..-.3Bof

i "Referringtoethe t controlrcirenit'` 14,{1TableI-gshows a chart V ottlie-positionsjofjrelays thro ugh YR5 for the variousseguentialesteps1of the operation 'ofthe' control circuit of PigijBBlThelirstfcolumn*iridicatesitherelay -referredjtonVandtheseetnrdcolnrnnshows that'inithennenergized stateali the-relaysareein the-open position.

Y`Asecan beA seen *from'lable I f n1d"'frf.rrr1 Fig.V Slvvhichgraphically?'showsfthe closed and open positions ofthe relaysg`frelays-2,3, and 4 :are sogar-ranged that once'they are energized" they stayclosedfon -theremainder fof; Ithe cycle. However,:relaylR11isV4concerned with the verifica- Ytioncircuit including-I the-recordingO'boththe -diastolic -and -systolicpressurea-n'd is therefore repiiredto close and open twice during the iblood-pressure readingrcycle. vRelayR5 i s concerned -with thesatety vfeature of the normally-open-rapidfdeilationrvalve 39, an'd'it is there-"foreerequired-thatthis valve -be vopen-when no poweris Ybeginninggof'the Acycle so@thatfpressnrecanlhuild Vup in thereservoirhut-it -must -open a t the -end Y of -t-he cycle toprovidei'fforrapid d eation-of the -cut once the readings `havebeenjt-aken.

-Referring'backftoFigs '3A43C5 the measuringcycle vis initiatedeithereby nianual-.s-Witch-Sl or program switch S2. V*This is.'vaccomplished Iby breaking momentarily the v250- volt -powersu-pply tothe-cireuit and allowingtherelays R2, R3, and B4, whichwereclosed^at=the end -ofjthe fprevions cycle-to assume theirunenergizedoropen position. The programm-ingswitchSZ may be actuated'-byf a Ytirnecicam eranyfother suitable timing device.

A When either SI-or-S2 is openedfthe'relays 'R2 and R4 assume-the open-or-unenergized positions, since no B+ power is supplied#tothe-'control'circuiti-through t-he switches. lWhentheyswit-ch is released, power is'supplied totthecontrol circuit andrelaysf R1, R2, and-R4- remain-open,relay 'R-g vopens--'and-rf :lay YRSL closesj in `1 -manner ito beexplained later. 37B shows the relayeswitches'es -theyappear-fratgthe#beginning of fa- 5 R rRfop enan'd-relay fRsfclose'd. i Y

1 The Vcycle commences :when :either the switch S1 forsSz:i.s-m9.n.1eatari1yt0pened,@attention.closingaptessure starts -eyclewithrelays f 1 9 to build up in the system. No sound is heard on themicrophone until the diastolic pressureis reached, and it is therstsound from the microphone gated by the pressure pulse that initiallyserves to activate relay R1.

AssumingV that a pulse is receivedV simultaneously from both themicrophone circuit and the pressure gating circuit, then theVcoincidence circuit passes a signal pulse to the control circuit. Sincetube T2 is normally conducting, a pulse on the grid of T1 raises theslightly negative bias on the grid of that tube so that current passesthrough both T1 and T2, and relay R1 is energized.

rTheV relay switches are grouped4 according to the relays that activatethem. When relay R1 closes the three switches, R181, R1S2and R183 areactivated. The closing of R181 places B+ 250 volts supplied via; thepower supplyl line` 64 through the lower Contact of R181 on the platevof delay tube T3, whosev functionvwill be explained ater.

AsV can be seen, voltage source 6) provides4 +24 volts viav lead 65, theupper contact of R182, lead 66, and the upper contact of R382to activateand hold open inllation valve 2 so the pressure in the system maybuildup. The closing of R182 breaks this connection, closing valve 2 andmaintaining the pressure in the system constant. With the center contactof R182 in its, lower position, source 6i) now supplies +24. volts via.`thevlower contact of R182, lead 67, the upper contact of R381, and lead69, to the diastolic valve 16, thus opening it and allowing meter 17torrecord the pressure.

The; closing of R183 removes the negative bias oi" -150 volts from B+supply 79 that has been applying a large negative voltage to bias tubesVT4 and Tf1 through lead 71. With the negative bias onV the gridl of tubeT4 slowly decreased to about -30 volts, this tube can nowl be renderedconducting by the incoming pulses that are being supplied; to it,thusactivating andA closing relay R2. The negative bias from source 7)is normally applied acrossresistor 91 and the parallel combination ofcapacitor 92 and resistor 93 by way of lead 7i so that the tubes arebias-ed approximately at 150 volts. However, withR183 closed the -150volts is applied across resistor 94. and the parallel combination ofcapacitor 92 and resistor 93. The values of resistors 9T., 93', and. 94,are chosen so that the voltage appearing at the junction of resistors 93and 94 is approximately -30 voltsv or about one-fifth of its previousmagnitude. Capacitor 92 provides a slight delay inthe bias voltagechange to provide time for the veriiication (which will be explainedlater) to take place.

The closing of R281 removes B+ from tube T1, thereby deactivati'ng'relayR1 and resetting it in the open position. Relay switch R281y places thisB+ on the plates of T and T5 which act together as a pulse-absencedetector. The closing of R282 breaks the +24-volt circuit to the coil ofvalve 1'6' and closes that Valve, thus capturing the diastolic pressurereading.

Itshould'be noted that the resetting of.' relay R1 restores the originalfunction of its relay switches and resets it so that it would' again besensitive to pulses except for the fact that there is no connection forthe B+ supply to the plate of tube l, this connection having been brokenby the closing of R281.

'The point in the cycle has been reached where the diastolic pressurehas been recorded, and the pressure in the system is increasing to thesystolic range where the sounds will disappear.

With R281 placing B+ on the plates of both tubes T5 and' T5, these tubesboth are capable of being rendered conductive by overcoming the negativebias on each grid. The bias on tube T5 is overcome with each pulsecausing this thyratron tube to tire with the incoming pulses. ln betweenpulses the voltage across capacitor 96 builds up only to be dischargedthrough the tube as it lires. However, when the incoming pulses die outtube T5 no longer, lires, and the voltage across capacitor 96 increases`to a large value raising thepotential. 011` the l grid of thyratron tubeT5, causing this tube to fire and thus activating relay R3. Thepulse-absencev detector 28, including tubes T5 and T5, maintains R3`unactivated during the reception of pulses but a short time after thepulses die out (which depends on the charging time constant of capacitor96 in series with resistors 97 and 98.) the pulse-absence, detectorcauses relay R3 to be actuated.

The tiring of tube T5 energizes relay R3. The closing of relay switchR3S1serves no immediate useful purpose, since R182is in the, up, oropen, position, and lead 67 is not connected to any, potential source atits upper end. The activationof R382I transfers +24 volts from theinflate; coil to' the; deate: coil, causing the ormerto close and thelatter to open.

R383 serves to place B+ back o-n T1 by way of, lead 73, readying thistube and its associated circuit for the reception of the; rst systolicpressure sounds as the pres.- sure decreases from Eto F in thel graph ofFig. lA. R384 places B+ on Tfpvia lead 74, likewise readying this tubefor the first pulse sounds at the systolic pressure.

Qn reception ot pulses at the systolic pressure value, realy R1 closesand- R181 again places B+ on the time delay for purposes to beexplainedlater. R182l again closes, placing +24 volts on the systolic valveactuating coil, causing valve 19 tol open. This connection isf madevialead 67 throughthe` lower contact of R381, which now serves thepurposefor which it previously closed, through lead 72 and on to thesystolic valveV solenoid' R185 again removes the large negative biasfrom the tubes including t-ube, T7, whichis made readyV to function.

Now with B+ applied by the closure of R384, tube Tf1 can be renderedconducting upon the receipt of pulses from multivibrator 26. Thisenergizes relay R4, which closes 12.481 placing.; B+ on resistor 76 viathe: lower contact of R384, lead 7-7, R481, and lead- 7S, causing theclosure of'relay- R4. Switch R282 breaks thecircuit to the systolicvalvev actuatingcoil, causing valve 19, to close, and` the systolicpressure to be captured? by-meten 20.

SwitchY R483 removes B+ from relay R5 -supplied thereto by lead 79,causing relay R5 to be rie-energized and to open. The relay R5 is of;the slow release type, allowing time for ally actions to be completebefore end;- ingfthecycle.

After the short delay whenV R5 opens, switchV R581,y re.- moves the` +24volts from the rapid deflate solenoid, causing valve 39l to return toits unenergized; open state and rapidly exhaust the pressure system. Itralso places the +250 volts from source itil on the cycle-complete lamp81, causing it to light.

Ignoring R582 for the moment, R583 serveszto remove B+ from tube so thatany remote possibility ofr a relay cycle being inadvertently initiated,causing the: relays to chatter, is completely eliminated.

Switch R583 along with R582 serves anz additional very importantVpurpose. Sincerelay. R5 controlsnormally open valve 39, itsunenergizedstate must be open; that is, when no energy is supplied to the circuit,it mustl beropen, Furthermore, it mustalso function tol open at the endof the cycle to exhaustv the pressure from the system. Thus it isrequired, to be open. when the circuitisv not energizedl (e. g., powerfailure) and is also to go from closed to open atthe endof the cycle, atwhich time. the circuit is energized. In other words, relay R5 must beclosed immediately upon the application of energy to the unit.

Such action is accomplished by lead Sil. Since R583 normally restsagainst' its lower contact, any B+ applied to the circuit will becarriedv by lead 86 to resistor 76. This means that R4 is energized themomentthe circuit is plugged into a voltage supply. The closing of R11assures that R5 will' remain open for the time that the circuit isenergized but during which no cycle is initiated. In` this way4 itis`impossible for pressure to build up in the system when the device is.:plugged in but not being since relay R4 has no such delay circuit.

1 l usedysince, with relay Rf, positively positioned closed, relay R Visheld open, thusl keeping yrapid deflate valve 39 open. v Likewise R582places vB-lon tube v'Isfvia lead 82, causing relay R3 to`close and putsB+ on resistor 83, vclosing relay R2. Y

In other words, R582 and R583, since they are in the normally open ordown position, are used to position-the relays in the end-of-cycleposition immediately upon pluggingfin the device to a voltage supplybyclosing'relays R2-R4. Then, when `either S1 or S2 is momentarily opened,relays R2 and R4 are deenergized open and assume the start-of-cycleposition. The switch opening causes R5 to be energized from separate B+source 101, causing R5 to close and likewise assume its startof-cycleposition.

'In orderto insure that with the initial energization of the circuitrelay R5 will be open, a time delay consisting of resistor 102 i'andcapacitor 103 is incorporated in the circuit lof relay R5. Thus pluggingin the circuit will serve to close relay R4 through'R5S3 andV lead82,

relay R4 is closed before relay R5 has a chance vto close. As can beseen from the drawing, the closure of R4 by means of switch RSa'removespower from Arelay R5 and insures that it will remain open until relay R4is subsequently opened -upon the initiation of a measuring cycle. It hasbeen Anoted. that applicants invention incorporatesa verification, fortime delay, in the pressure'system before veach pressure reading. Thisis accomplished by means vof'tube T3 shown in Fig. 3B. Upon4thereception of the rst diastolic pressure value pulse, for example, T1

conducts, closing Yrelay R1 and opening the diastolic valve 16.Likewise, the pressure inflation valve is closed, and the increase inpressure of the system halted. If a second pulse is received withinapproximately 1.5 kseconds the cyclecontinues,as has been described. IfVnovsecond pulse is receivedthe voltage applied through `RlSlcausescapacitor-85 to'charge positively through resistors 86 and v87.. TheR-'C time constant of this circuit is Vchosen as about 1.5.seconds, ormore than a suicientA time for a -second pulse to bereeeived aspreviously` explained. After approximately -1.5 seconds, the voltageacross capacitor `85 builds up, causing T3 ltoire. This results vin anegative pulse from the plate of T3 to the grid Vof tubeT2 rendering T2vnonconducting and` deenergizingvrelay R1. =With relay R1 againopened,the inflation'vvalve 2 reopens andthe pressureresumes its gradualrise. Likewise'valve @16"i's closed awaiting a .new ,higher diastolic.pressure reading. This circuit operates similarly YVfor-the .systolicpressure reading. Y

llressureiswitch Y104 isan adjustable safety'swit'ch whose contactsopenwhen apreset pressure has been exceeded. =In normal use a setting vwouldbe made ywhich allows a margin of at least 30 mm.:above the maximumanticipated systolic pressure. Theactuation of switch .104 opens R5Whichybrings the systemv to the state which it normally reachesrat-theendrofy a measurement cycle. Under'this condition, as hasVbeenydescribed previously, the rapid deate'valve -39 is'open and thecuff deflated. The systemis then in Vstand-by condition in readiness` togo 'through the next measurement cycle, when initiated.

In putting the system into operation after attachment of the cu andmicrophone, it is only necessary to adjust the gain in thesystem` to thecharacteristic sound level of the subject. First the ausculatorydiastolic pressure is determined. The cuff is then inflated to thisvalue, and held while the gain control is increased until the thresholdindicator begins to ,pulsate .This is the V,proper gainsetting forthesubject, anditis left undisturbed vafter-the initial setting.

T 'Iherinstrument has beenV used-,onY many. different-sub- .jects .orvperiods ranging 'from -.an hour to v`as. long g as i l 8 hours underhospital conditions. 1n general, there `appears to be no patientdiscomfort Aandafter an Yinitial In this wayV bedpatient isundisturbed.V

Y'Preliminary work shows thatnthere. is a-good` agreement of theinstrument valuesl fwith ausculatoryA values over the full-range ofpressures encountered in'normals andhypert'ensives. Changes in pressure.followingthe administrationV ofy drugs atecting'blood pressure arefollowed by the instrument. Atpresent the programming switch repeatsVthe measurement cycle once everyrthree minutes. The actual determinationtakes about `one minute or less for the normal range of pressures butVis dependentV upon the maximum pressure `the system--must reach.

The important featuresrof applicants invention may be summarized asfollows: Y Y

(1)' The captured pressure arrangement `makesit possible to obtainand-hold or Vrecordthe diastolic and systolic blood pressure readings.(2) Thefeaturel ofV increasing the Vpressure ybeyond th systolic rangeand then decreasing it provides a more accurate determination of thesystolic pressure'value. (3). Applicants control Ysystem is entirelyelectrical utilizing commercially available components, thus vmal:- ingit more economical to manufacture. f

(4). The rapid increasegof pressure to apoint just below thepredetermined diastolic level allows the cutrto be inated for a shorterperiodk of-time.

. (5) Three safety features incorporated inapplicants device: (a) theelectrical maximum-pressure control,.(b)

made. Instead of the captured pressure type meters17 and 20 anyconventional type recording meter Ymight be actuated by thesignals tovalves 16 and 19 providing y a display of the Ydiastolic and systolicpressure values.

Likewise the position of microphone llcould be placed at variouspositions on arm 42 to provide optimum sound pick-up including placingVit directly under the occluding cui 4. VThese and otherobviouskmodifications are felt to be within the scope of the presentinventionas defined in the appended claims. What is claimed is:

l. An automatic sphygmomanometer including an oc cluding cuff, meansforperiodicallyinilating and deating said .cuit over a range ofpressures including the kdi- ;astolic `andlsystolic rpressures of asubject `being tested, -auscnlatorygmeans forV obtaining electricalsignalsrat said diastolic and systolic pressures, timesensitive gatingmeans 4coupledrto saidcut for gating outznoise signalspassingwthroughsaid Aausculatory means and means fre- .sponsive to said.electrical signals Afor recording lsaid .diastolic and systolicvpressure values V2.A An automatic sphygmomanonieteri comprising lanoecluding cuil, means for rapidly inilating.-,Said lCini to apredetermined pressure /just below.` the; diastolic pressure l of vasubject.beingY tested,- meansior-.inatina and subsequently deating saidcu over -a pressure range including said diastolic and the systolicpressures ofa humanbeing,

.ausculatoryemeans forg nbtaining .electrical signals aty saidVYdiastolic and .systolicV pressures. means including a hermStor tLansd11C1forggatingout*noise signals picked Yup `bysaid Iausculatory means..means resncnsive tesaid .electrical signalsL-for.;r ec0rdina:saiddiastplieand -lsustolic pressure valuesirandmeans.fforrapidly-deating.-saidcuff. 3.Anrautornatic:sphyjgmornanometer'comprising.anoc- .cluding cuff, ,meansfor inflating Vand-subsequently. deatingsaid cuff oyera range.cipressures iincludingvthe aar-modo diastolic and systolic pressures ofa human being, micron phone means for obtaining electrical signals atsaid diastolic and systolic pressures, means for gating out most of thenoise signals picked up by said microphone means, verification means foreliminating undesired signas passed by said gating means and meansresponsive to said electrical signals for recording said diastolic andsystolic pressure values.

4. An automatic sphygmomanometer as deiined in claim 3 in which saidrecording means includes means for directly displaying the diastolic andsystolic pressure values.

5. An automatic sphygmomanometer comprising an occluding cuif, means foriniiating and subsequently defiating said cuff over a pressure rangeincluding the diastolic and systolic pressures of a human being,microphone means for obtaining electrical signals at said di astolic andsystolic pressures, means for gating out most of the noise signalspicked up by said microphone means, verification means for eliminatingundesired signals passed by said gating means, means responsive to saidelectrical signals for recording said diastolic and systolic pressurevalues and means for starting a new measuring cycle after apredetermined length of time.

6. An automatic sphygmomanometer comprising an occluding cuff adapted tobe placed over the artery of a human being, means for iniiating andsubsequently deflating said cuif over a pressure range including thediastolic and systolic pressures of said human being, microphone meansadjacent said cuff for deriving rst electrical signals from said arteryincluding means to detect sounds at said diastolic and systolic pressurelevels, means for detecting the variations in pressure in said occludingcufr due to pulsation of said arter, transducer means for convertingsaid pressure variations into second electrical signals, means forgating said first signals by said second signals, verication mean foreliminating noise components of said first signals passed by said gatingmeans and means responsive to said iirst signals for recording saiddiastolic and systolic pressure values.

7. An automatic sphygmomanometer comprising an occluding cuff, pressuresensing means, means for iniiating and subsequently deiiating said cuiover a range of pressures including the diastolic and systolic pressuresof a subject being tested, means connected to said sensing meansincluding a transducer for obtaining first electrical signals at saidmeasured diastolic and systolic pressures, ausculatory means forobtaining second electrical signals at said distolic and systolicpressures, coincidence means responsive to said iirst and second signalsfor deriving an output upon concurrence of said signals and meansresponsive to said output signals for recording said diastolic andsystolic pressure values.

8. An automatic sphygmomanometer as defined in claim 7 in which saidrecording means includes means for permanently displaying a directrepresentation of said diastolic and systolic pressure values.

9. The device as defined in claim 8 including means for rapidly deatingsaid cuit at the end of a measuring cycle.

10. The device as defined in claim 9 including means for initiating anew measuring cycle after a predetermined length of time.

11. An automatic sphygmomanometer comprising an occluding cuff forapplication over an artery in a limb of a human being, means for rapidlyiniiating said to a predetermined pressure below the diastolic pressureof said human being, means for inflating said cuff at a slower rate andsubsequently deating it at said slower rate over a range of pressuresincluding said diastolic and the systolic pressures of said human being,microphone means adapted to be attached to said limb adjacent said culfor detecting sound pulses caused by the occlusion of said artery andconverting them into first electrical signals, means for detecting thevariations in pressure in said occluding cuff due to pulsation of saidartery, transducer means including a thermistor for converting saidpressure variations into second electrical signals, gating meansrendered conductive by said second electrical signals so that signalspass through said gating circuit only when they occur at the same timeas said second signals, control circuit means for operating recordingmeans whch provide a permanent record of said diastolic systolicpressure values and verification means coupled between said gating meansand said control circuit means for rendering said control meansinoperative if more than one pulse is not transmitted through saidgating means over a predetermined period of time.

l2. An automatic sphygmomanometer comprising an occluding cuff forapplication over an artery in a limb oi a human being, means forcoupling said culi" to an air reservoir, compressor means for rapidlyincreasing the pressure in said cuff and reservoir to a predeterminedpoint below the diastolic pressure of said human being, means inconjunction with said pressure means for more slowly increasing thesystem pressure over a range including said diastolic and the systolicpressure of said human being, a microphone adapted to be attached tosaid limb adjacent said cuit for detecting sound pulses caused by theocclusion of said artery and converting said pulses into firstelectrical pulses, a thermistor transducer for detecting the pressurevariations in said artery transmitted by said occluding cuir" andconverting said pressure variations into second electrical pulses, agating circuit coupled to the output of said microphone and saidthermistor transducer, variable delay means coupled between saidmicrophone and said gating circuit for adjusting the phase of said iirstelectrical pulses applied to said gating circuit to equal the phase ofsaid second electrical pulses applied to said gating circuit, saidgating circuit producing output pulses only when pulses received fromsaid microphone and said thermistor transducer are in phase, iirst meansresponsive to said gating circuit output for recording said diastolicpressure value, means for slowly decreasing said system pressure over arange including said systolic pressure, second means responsive to saidgating circuit output for recording said systolic pressure value, meansfor holding said system pressure constant during the recording of saidpressure values, and verification means coupled between said gatingcircuit and said recording means for rendering said recording meansinoperative when a iirst gating circuit output pulse is not followed bya second similar pulse in a predetermined time.

13. A device as defined in claim 12 in which said predetermined time isapproximately 1.5 seconds.

14. A device as defined in claim 13 including means for rapidlydeiiating said system pressure after the systolic pressure value isrecorded.

15. A device as defined in claim 14 including means for automaticallyrepeating the recording of said diastolic and systolic pressuresapproximately every three minutes.

16. A device as dened in claim l5 in which said rst and second recordingmeans include means for providing a permanent direct display oi' saiddiastolic and systolic pressure values.

References Cited in the le of this patent UNlTl-ED STATES PATENTS2,053,383 Telson et al. Sept. 8, 1936 2,272,836 Gerdien Feb. l0, 19422,571,124 Farrand Oct. 16, 1951 2,710,001 Freyburger lune 7, 1955

